It is possible to make the crude assumption that global energy use will double by 2050. If there are the expected improvements in the efficiency of fossil fuel use and a continuing shift from coal to gas, fossil fuels should be providing no more than 30% of global energy in 2050 to achieve the required reductions in greenhouse gas emissions. Sources that do not emit greenhouse gases (renewables and nuclear power) would have to grow by a factor of about 15 from 2000 levels for this to happen, or by a factor of 50 if nuclear power is excluded. Against this background, a reappraisal of all approaches to providing energy is essential. This reappraisal must determine what actions are required in the near future to ensure that sufficient supplies and types of energy will be available to meet both growing world demand and greenhouse gas emission constraints. There are four major options to address these challenges: 1. Demand-side measures to reduce energy requirements. 2. Nuclear power. 3. Renewable energy sources. 4. Sequestration of GO_2 produced during the use of fossil fuels. Although these options are sometimes seen as being in competition, this is by no means necessarily the case. It is quite probable that some combination of all four will be needed.
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